COVID-19 booster uptake among US adults: Assessing the impact of vaccine attributes, incentives, and context in a choice-based experiment.

Objective: Evidence shows that booster shots offer strong protection against the Omicron variant of COVID-19. However, we know little about why individuals would receive a booster compared to the initial decision to vaccinate. We investigate and assess the factors that affect individuals' reported willingness to receive the COVID-19 vaccine booster. This information can aid in tailoring public health messaging to communicate attributes that are associated with individuals' attitudes toward the COVID-19 booster.

Rationale: Existing research provides little insight into whether the same factors that affect Americans' likelihood of accepting initial vaccination against COVID-19 also affect booster uptake. Our experiment also examines the influence of contextual information about a novel variant on willingness to receive a booster.

Methods: We administered a conjoint experiment (N = 2740 trials) in a survey of fully vaccinated US adults that had not yet received a COVID-19 booster (N = 548) to assess the impact of varied vaccine attributes on willingness to receive a booster.

Results: The most important factors associated with higher willingness to receive a booster were efficacy, manufacturer, and the size of a financial incentive. Protection duration and protection against future variants vs. only current variants had modest influence. A contextual prime reporting that some public health experts believe the Omicron variant is more contagious, but less lethal than those previously seen, significantly increased favorability toward boosters. This provides potential motivation and guidance for vaccination campaigns to emphasize these variant-specific traits.

Conclusion: With several vaccines with varying degrees of efficacy available to consumers, emphasizing boosters with a high efficacy would likely improve attitudes toward boosters. Financial incentives and predispositions toward manufacturers also matter. Concerns about more contagious variants may spur uptake, even if such variants are less lethal.